1. Field of the Invention
The present invention relates to an illumination device having a light guide body which serves as a sheet-like or a strip-like light-emitting face.
2. Description of the Related Art
In recent years, there have been frequently used a light emitting diode (hereinafter, sometimes referred to as an “LED”), a cold cathode tube or the like as a light source for illumination due to a higher luminous efficiency. However, the LED, which is a point light source, is of directivity, thus finding only a limited use as an independent spot illumination. The cold cathode tube represented by a fluorescent lamp is used widely as a light source in general. When the cold cathode tube is used as a uniform sheet-like light source, there is adopted a method in which many cold cathode tubes are arranged to have diffusers disposed in front of them. However, this method poses such a problem that the effective use of space is lost.
As such, light guide-type illumination devices in which techniques for a light guide plate and a light pipe represented by a backlight for a liquid crystal display are used to convert a point light source such as LEDs to a line light source or convert a line light source, such as cold cathode tubes, to a sheet-like light source have been adopted.
Illumination includes not only static lighting uses in general but also lighting uses represented by neon signs which make dynamic expressions. The dynamic lighting uses include indicators for vehicles, and an illumination device excellent in appearance and visibility has been disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-83776, for example.
However, where the above-described dynamic expressions are made, for example, by using an LED, a plurality of the LEDs are prepared, and then the LEDs are illuminated by turns. Specifically, an illumination device is able to make one-dimensional expressions by arraying many LEDs linearly and also able to make two dimensional dynamic expressions by arraying many LEDs in a sheet-like manner (so called image expression). However, the above method for giving a difference in time interval requires many LEDs densely disposed and also requires a power source for driving each of the LEDs. For example, if the above method for illuminating the LEDs by turns is used in a case where expressions of relatively simple and patternized motions such as interior signs, indicators of vehicles and displays of signboards are sufficient, the costs to be perform the method reduce the effect.
On the contrary, if an illumination device is lit by using a small number of LEDs for the purpose of reducing the cost, a problem is posed in that no smooth motions are realized or in that brightness varies easily (hereinafter referred to as “variance in brightness”) in an attempt to obtain a uniform distribution of brightness in a static state. In order to suppress the above-described variance in brightness, there is another method in which light sources such as LEDs or electric bulbs are made uniform to dispose the light sources and optical elements including a diffuser. However, this method requires a specific space between the light source and the optical element, consequently contributing to a large-sized illumination device.
Further, Japanese Patent Application, First Publication No. 2003-83776 has disclosed that luminous bodies (light guide bodies) disposed adjacently in a concentric manner are lit on and off sequentially. However, in order to eliminate variance in brightness, it is necessary to densely dispose the luminous bodies and also dispose diffusers in front of them. Thus, there is provided no solution for removing the disadvantage of higher costs.
The present invention has been made in view of the above circumstances, an object of which is to provide an illumination device capable of making dynamic expressions at lower costs and also suppress variance in brightness.